Circumferential back-to-back seal assembly with bifurcated flow

ABSTRACT

A circumferential seal assembly capable of separating a gas into two separate flow paths before communication between a rotatable runner and a pair of seal rings is presented. The seal assembly includes an annular seal housing, a pair of annular seal rings, a rotatable runner, and a plurality of groove structures. The seal housing is interposed between a pair of compartments. The seal rings are separately disposed within the seal housing and separately disposed around the rotatable runner. The groove structures are disposed along an outer annular surface of the rotatable runner. A gas is communicable onto the groove structures. Each groove structure includes at least two hydrodynamic grooves that separate and communicate the gas onto the seal rings. Each groove includes steps whereby the depth of at least one adjoining step decreases in the direction opposite to rotation with or without the depth of another adjoining steps increasing in the direction opposite to rotation. Each groove is also tapered widthwise.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/845,947 filed Sep. 4, 2015 which is a continuation-in-part of U.S.patent application Ser. No. 14/396,101 filed Oct. 22, 2014 now U.S. Pat.No. 9,194,424 which is a National Phase of PCT Application No.PCT/US2014/033736 filed Apr. 11, 2014 which further claims priority fromU.S. Provisional Application No. 61/811,900 filed Apr. 15, 2013, eachentitled Circumferential Back-to-Back Seal Assembly with BifurcatedFlow. The subject matters of the prior applications are incorporated intheir entirety herein by reference thereto.

FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

None.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention generally relates to a circumferential seal assembly withbifurcated hydrodynamic flow for use within a gas turbine engine andmore particularly is concerned, for example, with a pair of annular sealrings separately disposed within an annular seal housing about arotatable runner attached to a shaft, wherein the runner furtherincludes a plurality of stepped and tapered hydrodynamic grooves whichseparate and direct flow onto each annular seal ring to form a pair ofthin-film layers sealing one compartment from another compartment.

2. Background

Turbine engines typically include a housing with a plurality ofcompartments therein and a rotatable shaft that passes through adjoiningcompartments separately including a gas and a lubricant. Leakage of alubricant from one compartment into another compartment containing a gascould adversely affect performance and function of a gas turbine.Leakage of a gas from one compartment into another compartmentcontaining a lubricant is likewise detrimental. As such, adjoiningcompartments must be isolated from one another by means of a sealingsystem that prevents one fluid, either a lubricant or a gas, frommigrating along a rotatable shaft and entering a compartment so as tomix with another fluid therein.

In the case of an aircraft engine, leakage of a lubricant or a gasacross a seal into a neighboring compartment may cause oil coking or anengine fire. Oil coke is a byproduct formed when an oil lubricant and agas mix at a temperature that chemically alters the oil. Oil coke canfoul sealing surfaces thereby degrading bearing lubrication andimpairing the integrity of a seal. It is important in similarapplications, not just aircraft engines, that a lubricant be isolatedwithin a lubricant sump and that a seal around a rotating shaft notallow a lubricant to escape the sump or a hot gas to enter the sump.Many applications will include either a circumferential seal or a faceseal to prevent mixing of an oil lubricant and a hot gas; however,circumferential shaft seals are the most widely used under theabove-noted conditions.

Various circumferential seal systems are employed within the art to forma seal between a compartment containing a gas at a high pressure and acompartment containing an oil lubricant at a low pressure. Sealingsystems typically include grooves disposed along an inner annularsurface of a seal ring to form a thin-film layer between the seal ringand a shaft.

Presently known circumferential seal designs are problematic when bothadjoining compartments are at a low pressure. The absence of asignificant pressure differential between compartments does not permitformation of a thin-film layer adequately capable of preventingmigration of a fluid along the interface between a seal ring and ashaft.

Presently known circumferential seal designs are further problematicwhen used in conjunction with a translatable runner. The temperaturesand/or mechanical loads within a turbine engine often cause a runner,and sealing surface thereon, to translation along the axial dimension ofan engine. The result is a sealing interface that is difficult tooptimize over the operational range of a turbine engine.

Accordingly, what is required is a circumferential seal assemblyinterposed between a pair of compartments that minimizes degradation toand/or failure of a seal between a rotatable runner and a pair of sealelements.

SUMMARY OF THE INVENTION

An object of the invention is to provide a circumferential seal assemblyinterposed between a pair of compartments that minimizes degradation toand/or failure of a seal between a rotatable runner and a pair of sealelements.

In accordance with some embodiments of the invention, thecircumferential back-to-back seal assembly includes an annular sealhousing, a first annular seal ring, a second annular seal ring, arotatable runner, and a plurality of groove structures. The annular sealhousing is interposed between a pair of compartments. The first andsecond annular seal rings are disposed within the annular seal housing.The first and second annular seal rings are disposed around therotatable runner. The groove structures are disposed along an outerannular surface of the rotatable runner. The gas is communicable ontothe groove structures. Each groove structure separates the gas so that afirst portion of the gas is directed onto the first annular seal ring toform a first thin-film layer between the rotatable runner and the firstannular seal ring and a second portion of the gas is directed onto thesecond annular seal ring to form a second thin-film layer between therotatable runner and the second annular seal ring. Each groove structurehas at least two grooves. Each groove includes at least two adjoiningsteps wherein each adjoining step has a base disposed at a depth. Thedepth decreases from at least one said adjoining step to another saidadjoining step in the direction opposite to rotation. A shoulder isdisposed between two adjoining steps whereby the shoulder locallyredirects the gas outward toward the first annular seal ring or thesecond annular seal ring so that flow of the gas is turbulent. Eachgroove is also tapered widthwise. Each groove is separately disposedabout a central axis aligned adjacent to the first annular seal ring andthe second annular seal ring. Each groove is disposed substantiallyparallel with respect to rotational direction of the rotatable runner.Each groove is communicable with a feed groove which directs the gasinto the grooves.

In accordance with other embodiments of the invention, the depthincreases from at least one adjoining step to another adjoining step inthe direction opposite to rotation. In accordance with other embodimentsof the invention, the seal assembly further includes a plurality ofsprings. The springs are disposed between and directly contact the firstand second annular seal rings. The springs separate the first and secondannular seal rings.

In accordance with other embodiments of the invention, a center ring isdisposed within the annular seal housing between the first annular sealring and the second annular seal ring.

In accordance with other embodiments of the invention, the seal assemblyfurther includes a center ring and a plurality of springs. The centerring is disposed within the annular seal housing between the first andsecond annular seal rings. The springs are interposed between the centerring and each of the first and second annular seal rings. The springsseparate the first and second annular seal rings away from the centerring.

In accordance with other embodiments of the invention, the grooves varylengthwise.

In accordance with other embodiments of the invention, adjacent groovestructures vary widthwise.

In accordance with other embodiments of the invention, the grooves areseparately disposed about a central axis aligned adjacent to the firstand second annular seal rings. Adjacent groove structures vary in numberof grooves.

In accordance with other embodiments of the invention, the annular sealhousing includes a windback thread adjacent to the compartment includinga lubricant. The windback thread directs the lubricant away from thefirst and second annular seal rings.

In accordance with other embodiments of the invention, a plurality ofslots positioned along the rotatable runner cooperate with the windbackthread to sling a lubricant away from the first and second annular sealrings.

Several exemplary advantages are mentionable. The invention facilitatesa circumferential seal along a rotatable/translatable runner between apair of low pressure compartments that minimizes mixing of a lubricantand a gas within adjacent compartments. The invention facilitates acircumferential seal along a rotatable/translatable runner between apair of compartments that minimizes translational effects on sealingproperties. The invention minimizes contamination to a pairedarrangement of annular seal rings by a lubricant originating from acompartment. The invention minimizes wear along a back-to-backarrangement of sealing rings within a seal assembly.

The invention may be used within a variety of applications wherein asealing assembly including a pair of annular seals is disposed about atranslatable sealing surface between a pair of low pressurecompartments. One specific non-limiting example is a turbine enginewherein a seal assembly is disposed about a rotatable/translatablerunner.

The above and other objectives, features, and advantages of thepreferred embodiments of the invention will become apparent from thefollowing description read in connection with the accompanying drawings,in which like reference numerals designate the same or similar elements.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional aspects, features, and advantages of the invention will beunderstood and will become more readily apparent when the invention isconsidered in the light of the following description made in conjunctionwith the accompanying drawings.

FIG. 1 is an enlarged cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a gapwithin a seal housing disposed about a runner attached to a shaft (crosssection of annular seal assembly below centerline, runner, and shaft notshown) rotatable about a centerline within a turbine engine inaccordance with an embodiment of the invention.

FIG. 2 is a partial cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a gapwithin a seal housing disposed about a rotatable runner attached to ashaft (cross section of annular seal assembly below runner and shaft notshown) wherein an outer annular surface along the runner includes aplurality of groove structures separately disposed thereon whereby eachgroove includes at least two steps and each groove structurecommunicates with both seal rings in accordance with an embodiment ofthe invention.

FIG. 3 is a partial cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a gapwithin a seal housing disposed about a rotatable runner attached to ashaft (cross section of annular seal assembly below runner and shaft notshown) wherein an outer annular surface along the runner includes aplurality of groove structures communicable with a single annular groovethereon whereby each groove includes at least two steps and each groovestructure communicates with both seal rings in accordance with anembodiment of the invention.

FIG. 4 is an enlarged cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a centerring within a seal housing disposed about a runner attached to a shaft(cross section of annular seal assembly below centerline, runner, andshaft not shown) rotatable about a centerline within a turbine engine inaccordance with an embodiment of the invention.

FIG. 5 is a partial cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a centerring within a seal housing disposed about a rotatable runner attached toa shaft (cross section of annular seal assembly below runner and shaftnot shown) wherein an outer annular surface along the runner includes aplurality of groove structures separately disposed thereon whereby eachgroove includes at least two steps and each groove structurecommunicates with both seal rings in accordance with an embodiment ofthe invention.

FIG. 6 is a partial cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a centerring within a seal housing disposed about a rotatable runner attached toa shaft (cross section of annular seal assembly below runner and shaftnot shown) wherein an outer annular surface along the runner includes aplurality of bifurcated groove structures separately disposed thereonwhereby each groove includes at least two steps and each pair ofnon-intersecting groove structures communicates with both seal rings inaccordance with an embodiment of the invention.

FIG. 7 is a partial cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a centerring within a seal housing disposed about a rotatable runner attached toa shaft (cross section of annular seal assembly below runner and shaftnot shown) wherein an outer annular surface along the runner includes aplurality of bifurcated multi-groove structures separately disposedthereon whereby each groove includes at least two steps and each pair ofnon-intersecting multi-groove structures communicates with both sealrings in accordance with an embodiment of the invention.

FIG. 8 is a partial cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a centerring within a seal housing disposed about a rotatable runner attached toa shaft (cross section of annular seal assembly below runner and shaftnot shown) wherein an outer annular surface along the runner includes aplurality of multi-groove structures separately disposed thereon wherebyeach groove includes at least two steps and each multi-groove structurecommunicates with both seal rings in accordance with an embodiment ofthe invention.

FIG. 9 is a partial cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a centerring within a seal housing disposed about a rotatable runner attached toa shaft (cross section of annular seal assembly below runner and shaftnot shown) wherein an outer annular surface along the runner includes aplurality of bifurcated multi-groove structures separately disposedthereon whereby the multi-grooves form two separate substructures withineach multi-groove structure, each groove includes at least two steps,and each multi-groove structure communicates with both seal rings inaccordance with an embodiment of the invention.

FIG. 10 is a partial cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a gapwithin a seal housing with an optional windback thread disposed about arotatable runner attached to a shaft (cross section of annular sealassembly and runner below centerline and shaft not shown) and optionalslots positioned along one end of the rotatable runner adjacent to thewindback thread wherein an outer annular surface along the runnerincludes a plurality of multi-groove structures separately disposedthereon whereby each groove includes at least two steps and eachmulti-groove structure communicates with both seal rings in accordancewith an embodiment of the invention.

FIG. 11 is a partial cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a gapwithin a seal housing with an optional windback thread disposed about arotatable runner attached to a shaft (cross section of annular sealassembly and runner below centerline and shaft not shown) and optionalslots positioned along one end of the rotatable runner adjacent to thewindback thread wherein an outer annular surface along the runnerincludes a plurality of multi-groove structures separately disposedthereon whereby the grooves are tapered, each groove includes at leasttwo steps, and each multi-groove structure communicates with both sealrings in accordance with an embodiment of the invention.

FIG. 12 is a partial cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a gapwithin a seal housing with an optional windback thread disposed about arotatable runner attached to a shaft (cross section of annular sealassembly and runner below centerline and shaft not shown) wherein anouter annular surface along the runner includes a plurality ofmulti-groove structures separately disposed thereon whereby the width ofadjacent multi-groove structures vary, each groove includes at least twosteps, and each multi-groove structure communicates with both seal ringsin accordance with an embodiment of the invention.

FIG. 13 is a partial cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a gapwithin a seal housing with an optional windback thread disposed about arotatable runner attached to a shaft (cross section of annular sealassembly and runner below centerline and shaft not shown) wherein anouter annular surface along the runner includes a plurality ofmulti-groove structures separately disposed thereon whereby the numberof grooves within adjacent multi-groove structures vary, each grooveincludes at least two steps, and each multi-groove structurecommunicates with both seal rings in accordance with an embodiment ofthe invention.

FIG. 14 is a partial cross section view illustrating an annular sealassembly including a pair of annular seal rings separated by a centerring within a seal housing disposed about a rotatable runner attached toa shaft (cross section of annular seal assembly below runner and shaftnot shown) wherein an outer annular surface along the runner includes aplurality of bifurcated multi-groove structures separately disposedthereon whereby each groove includes at least two steps, eachmulti-groove structure communicates with both seal rings, and aplurality of through holes are disposed along the rotatable runner inaccordance with an embodiment of the invention.

FIG. 15 is a cross section view illustrating the annular seal housing,the center ring, and the rotatable runner with through holes wherein theholes communicate a gas through the rotatable runner and onto the outerannular surface of the rotatable runner so that the gas enters thestepped grooves along the rotatable runner for redirection onto theinner annular surface of a first annular seal ring and a second annularseal ring in accordance with an embodiment of the invention.

FIG. 16 is a cross section view illustrating a stepped groove with anexemplary profile whereby the depth of each adjoining step decreases inthe direction opposite to rotation in accordance with an embodiment ofthe invention.

FIG. 17 is a cross section view of a rotatable runner illustrating analternate stepped groove whereby the depth of at least one adjoiningstep decreases in the direction opposite to rotation and the depth of atleast one adjoining step increases in the direction opposite to rotationin accordance with an embodiment of the invention.

FIG. 18 is a cross section view illustrating dimensions along arotatable runner and a stepped groove for calculating the distance ratio(R) based on the adjusted radial distance (r−h) over the runner radius(r_(r)) whereby the upper distance ratio (R_(U)) corresponds to theshallowest step ((r−h_(min))/r_(r)) and the lower distance ratio (R_(L))corresponds to the deepest step ((r−h_(max))/r_(r)).

FIG. 19a is an enlarged view illustrating the length (L) of a groovestructure with stepped grooves aligned diagonal to the direction ofrotation in accordance with an embodiment of the invention.

FIG. 19b is an enlarged view illustrating the length (L) of a groovestructure with stepped grooves aligned along the direction of rotationin accordance with an embodiment of the invention.

FIG. 20 is an exemplary plot illustrating the distance ratio (R) forrotatable runners with a radius from 1-inches to 20-inches whereby theupper limit of the distance ratio (R_(U)) corresponds to a length (L) of0.5-inches and a minimum step depth (h_(min)) of 0.00001-inches and thelower limit of the distance ratio (R_(L)) corresponds to a length (L) of1.95-inches and a maximum step depth (h_(max)) of 0.1-inches.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to several embodiments of theinvention that are illustrated in the accompanying drawings. Whereverpossible, same or similar reference numerals are used in the drawingsand the description to refer to the same or like parts. The drawings arein simplified form and are not to precise scale.

While features of various embodiments are separately describedthroughout this document, it is understood that two or more suchfeatures are combinable to form other embodiments.

Referring now to FIG. 1, a seal assembly 1 is shown with an annular sealhousing 2, a first annular seal ring 3, and a second annular seal ring4, each disposed so as to be circumferentially arranged about arotatable runner 15 (not shown). Components are composed of materialsunderstood in the art. The rotatable runner 15 (see FIG. 2) is anelement known within the art attached to a rotatable shaft. Therotatable runner 15 is rotatable within a turbine engine via the shaft.A seal is formed along the rotatable runner 15 by each annular seal ring3, 4. The annular seal housing 2, annular seal rings 3, 4, and rotatablerunner 15 are aligned along and disposed about a centerline 14, oftencoinciding with a rotational axis within a turbine engine. The annularseal housing 2 is attached to components comprising the housingstructure 51 (generally shown) of a turbine engine fixing the annularseal housing 2 thereto. The housing structure 51 is stationary andtherefore non-rotating. The housing structure 51, seal assembly 1, andthe rotatable runner 15 generally define at least a first compartment 5and a second compartment 6. The configuration of the housing structure51 is design dependent; however, it is understood for purposes of thepresent invention that the housing structure 51 cooperates with the sealassembly 1 and rotatable runner 15 to define two separate compartmentswhereby a gas resides at a low pressure within one such compartment 5and a lubricant resides at low pressure within another compartment 6.

The annular seal housing 2 generally defines a pocket within which theannular seal rings 3, 4 reside. The annular seal housing 2 has aU-shaped cross-section opening inward toward the centerline 14. One endof the annular seal housing 2 could include an insert 7 and a retainingring 8 which allow for assembly/disassembly of the annular seal rings 3,4 onto the annular seal housing 2. The annular seal rings 3, 4 could befixed to the annular seal housing 2 via means known within the art tolimit or to prevent relative rotational motion between the annular sealrings 3, 4 and the annular seal housing 2. In one non-limiting example,a pair of anti-rotation pins 52 is secured to the annular seal housing 2to separately engage a pocket 53 along each of the first and secondannular seal rings 3, 4. Interaction between the anti-rotation pin 52and the pocket 53 functions as a positive stop to restrict rotation ofeach of the first and second annular seal rings 3, 4 with respect to theannular seal housing 2.

The first and second annular seal rings 3, 4 are ring-shaped elements.Each annular seal ring 3, 4 could be composed of at least two arcuatesegments which form a generally circular-shaped ring when assembledabout a rotatable runner 15. The segments of the first and secondannular seal rings 3, 4 allow for radial expansion and contraction bythe respective annular seal rings 3, 4 about a rotatable runner 15. Eachannular seal ring 3, 4, is generally biased toward a rotatable runner 15via a compressive force applied by a garter spring 10, 11. The garterspring 10, 11 could contact the outer circumference of the respectiveannular seal ring 3, 4 and apply a compressive force inward toward therotatable runner 15.

A plurality of springs 12 could be separately positioned between theannular seal rings 3, 4. The springs 12 could be evenly spaced about thecircumference of the annular seal rings 3, 4 so as to exert a generallyuniform separation force onto the seal rings 3, 4. The springs 12 couldbe a coil-type device which generally resists compression. Each spring12 could be attached or fixed to one annular seal ring 3, 4. Forexample, one end of each spring 12 could be partially recessed within apocket 54 along at least one annular seal ring 3, 4. Each spring 12should be sufficiently long so as to at least partially compress whenassembled between the annular seal rings 3, 4. This arrangement ensuresthat each spring 12 exerts a force onto the annular seal rings 3, 4causing the annular seal rings 3, 4 to separate, thereby pressing theannular seal rings 3, 4 onto opposite sides of the annular seal housing2. The separation force exerted by the compression spring 12 ensures agap 13 between the annular seal rings 3, 4.

At least one inlet 9 is disposed along an outer wall of the annular sealhousing 2. The inlet(s) 9 is/are positioned so as to at least partiallyoverlay the gap 13 between the annular seal rings 3, 4. Two or moreinlets 9 could be uniformly positioned about the circumference of theannular seal housing 2. Each inlet 9 is a pathway through which a gas iscommunicated into and through the gap 13 between the annular seal rings3, 4.

Although various embodiments are described including a gap 13, it isunderstood that the gap 13 as described in FIG. 1 is an optional featureand that such embodiments could include a center ring 25 with optionalgaps or optional holes 31 as shown in FIG. 4.

Referring now to FIG. 2, a seal assembly 1 is shown in cross-sectionalform disposed about a rotatable runner 15, the latter illustrated inside-view form. The rotatable runner 15 includes a plurality of groovestructures 17. The groove structures 17 are arranged circumferentiallyalong the outer annular surface 16 of the rotatable runner 15immediately adjacent to the seal assembly 1. The groove structures 17are positioned so as to communicate a gas onto the annular seal rings 3,4 as the rotatable runner 15 rotates with respect to the seal assembly1. In some embodiments, it might be advantageous for adjacent groovesstructures 17 to partially overlap as represented in FIG. 2. In otherembodiments, adjacent groove structures 17 could be arranged in anend-to-end configuration or with a separation between the end of onegroove structure 17 and the start of the next groove structure 17.

Each groove structure 17 further includes a pair of diagonal grooves 19disposed about a central axis 44 circumferentially along the outerannular surface 16 of the rotatable runner 15. The diagonal grooves 19could be aligned symmetrically or non-symmetrically about the centralaxis 44. Each diagonal groove 19 is a channel, depression, flute, or thelike disposed along the outer annular surface 16. Although the diagonalgrooves 19 are represented as linear elements, it is understood thatother designs are possible including multi-linear and non-linearconfigurations. The central axis 44 could align with the gap 13 betweenthe first and second annular seal rings 3, 4 or reside adjacent to thefirst and second annular seal rings 3, 4 to allow communication of a gasonto the groove structure 17 over the translational range of therotatable runner 15. The diagonal grooves 19 are oriented so that thetop of the left side extends toward the right and the top of the rightside extends toward the left. The inward oriented ends of the diagonalgrooves 19 intersect along or near the central axis 44 to form an apex18. The apex 18 is further oriented toward the rotational direction ofthe rotatable runner 15 so that the diagonal grooves 19 expand outwardopposite of the rotational direction. The dimensions and angularorientation of the diagonal grooves 19 and the apex 18 are designdependent and based in part on the translational range of the rotatablerunner 15, the widths of the annular seal rings 3, 4 and gap 13, theextent of overlap or non-overlap between adjacent groove structures 17,the pressure required to adequately seal the interface between therotatable runner 15 and the annular seal rings 3, 4, and/or other designfactors.

Each diagonal groove 19 further includes at least two optional steps 62a-62 d. Although four steps 62 a-62 d are illustrated along eachdiagonal groove 19 in FIG. 2, it is understood that two or more suchsteps 62 a-62 d may reside along each diagonal groove 19. Each step 62a-62 d corresponds to a change in the local depth of the diagonal groove19 relative to the outer annular surface 16. For example, if a diagonalgroove 19 includes two steps 62 a, 62 b, then one step 62 a would have afirst depth and another step 62 b would have a second depth. The depthsdiffer so that one depth is deeper and another depth is shallower. Inpreferred arrangements, the steps 62 a-62 d are arranged so that thechange in local depth from one step to another step results in astepwise variation along the length of each diagonal groove 19.

When the diagonal grooves 19 intersect at an apex 18 or the like, thefirst step 62 a may be located at the apex 18 and immediately adjacentto and communicable with the next step 62 b along each diagonal groove19 extending from the apex 18, as illustrated in FIG. 2. In otherembodiments, two or more steps may reside within the apex 18 and atleast one step along each diagonal groove 19. In yet other embodiments,one step 62 a may reside along the apex 18 and a portion of one or morediagonal grooves 19 and the remaining step(s) 62 b reside(s) exclusivelyalong each diagonal groove 19. Regardless of the exact arrangement, thesteps 62 a-62 d are arranged consecutively to effect a stepwisevariation of the depth along the length of each groove structure 17.

In the various embodiments, the gas could originate from a combustion ormechanical source within a turbine engine. In some embodiments, the gascould be a gas heated by combustion events within an engine andcommunicated to the inlet(s) 9 from a compartment adjacent to the firstand second compartments 5, 6. In other embodiments, the gas could beeither a hot or cold gas pressurized and communicated to the outlet(s) 9via a fan or a pump.

Referring again to FIG. 2, a gas enters the inlet(s) 9 and is directedinward across the gap 13 between the first and second annular seal rings3, 4. After exiting the gap 13, the gas impinges the outer annularsurface 16 of the rotatable runner 15, preferably at or near the apex 18or inlet end 45. The gas enters the apex 18 or inlet end 45 and isbifurcated by the groove structure 17 so that a first portion isdirected into the left-side diagonal groove 19 and a second portion isdirected into the right-side diagonal groove 19. The quantity and/orrate of gas communicated onto each of the annular seal rings 3, 4 may bethe same or different. The gas traverses the respective diagonal grooves19 and is redirected outward from the rotatable runner 15 at the outletend 46 of each diagonal groove 19. The gas exits the left-side diagonalgroove 19 and impinges the first annular seal ring 3 forming a thin-filmlayer 20 between the first annular seal ring 3 and rotatable runner 15,thereby separating the first annular seal ring 3 from the rotatablerunner 15. The gas exits the right-side diagonal groove 19 and impingesthe second annular seal ring 4 forming a thin-film layer 20 between thesecond annular seal ring 4 and rotatable runner 15, thereby separatingthe second annular seal ring 4 from the rotatable runner 15.

Referring now to FIG. 3, a seal assembly 1 is shown in cross-sectionalform disposed about a rotatable runner 15, the latter illustrated inside-view form, between a pair of compartments 5, 6. The rotatablerunner 15 includes a plurality of groove structures 17. The groovestructures 17 are arranged circumferentially along the outer annularsurface 16 of the rotatable runner 15 immediately adjacent to the sealassembly 1. The groove structures 17 are positioned so as to communicatea gas onto the annular seal rings 3, 4 as the rotatable runner 15rotates with respect to the seal assembly 1. In some embodiments, itmight be advantageous for adjacent grooves structures 17 to partiallyoverlap as represented in FIG. 3. In other embodiments, adjacent groovestructures 17 could be arranged in an end-to-end configuration or with aseparation between the end of one groove structure 17 and the start ofthe next groove structure 17.

Each groove structure 17 further includes a pair of diagonal grooves 19disposed about a central axis 44 circumferentially along an outerannular surface 16 of the rotatable runner 15. The diagonal grooves 19could be aligned symmetrically or non-symmetrically about the centralaxis 44. Each diagonal groove 19 is a channel, depression, flute, or thelike disposed along the outer annular surface 16. Although the diagonalgrooves 19 are represented as linear elements, it is understood thatother designs are possible including multi-linear and non-linearconfigurations. The central axis 44 could align with the gap 13 betweenfirst and second annular seal rings 3, 4 or reside adjacent to the firstand second annular seal rings 3, 4 to allow communication of a gas ontothe groove structure 17 over the translational range of the rotatablerunner 15. The diagonal grooves 19 are oriented so that the top of theleft-side extends toward the right and the top of the right-side extendstoward the left. The inward oriented ends of the diagonal grooves 19intersect an annular groove 39 along the central axis 44. The annulargroove 39 is a channel, depression, flute, or the like circumferentiallyalong the outer annular surface 16 of the rotatable runner 15. Althoughthe annular groove 39 is represented as linear elements, it isunderstood that other designs are possible including multi-linear andnon-linear configurations. The intersection point between the diagonalgrooves 19 and the annular groove 39 is oriented toward the rotationaldirection of the rotatable runner 15 so that the diagonal grooves 19expand outward opposite of the rotational direction. The dimensions andangular orientation of the diagonal grooves 19 and annular groove 39 aredesign dependent and based in part on the translational range of therotatable runner 15, the width of the annular seal rings 3, 4 and gap13, the extent of overlap or non-overlap between adjacent groovestructures 17, the pressure required to adequately seal the interfacebetween the rotatable runner 15 and annular seal rings 3, 4, and/orother design factors.

Each diagonal groove 19 further includes at least two optional steps 62a-62 d. Although four steps 62 a-62 d are illustrated along eachdiagonal groove 19 in FIG. 3, it is understood that two or more suchsteps 62 a-62 d may reside along each diagonal groove 19. Each step 62a-62 d corresponds to a change in the local depth of the diagonal groove19 relative to the outer annular surface 16. For example, if a diagonalgroove 19 includes two steps 62 a, 62 b, then one step 62 a would have afirst depth and another step 62 b would have a second depth. The depthsdiffer so that one depth is deeper and another depth is shallower. Inpreferred arrangements, the steps 62 a-62 d are arranged so that thechange in local depth from one step to another step results in astepwise variation along the length of each diagonal groove 19.

When the diagonal grooves 19 intersect an annular groove 39 or the like,the first step 62 a is immediately adjacent to and communicable with theannular groove 39 as illustrated in FIG. 3. The depth of the first step62 a may be deeper than, shallower than, or the same as the depth of theannular groove 39. Regardless of the exact arrangement, the steps 62a-62 d are arranged consecutively to effect a stepwise variation of thedepth along the length of each groove structure 17.

Referring again to FIG. 3, a gas enters the inlet(s) 9 and is directedinward across the gap 13 between the first and second annular seal rings3, 4. After exiting the gap 13, the gas impinges the outer annularsurface 16 of the rotatable runner 15, preferably at or near the annulargroove 39. The gas enters the annular groove 39 and is bifurcated by thegroove structure 17 so that a first portion is directed into the inletend 45 of the left-side diagonal groove 19 and a second portion isdirected into the inlet end 45 of the right-side diagonal groove 19. Thequantity and/or rate of gas communicated onto each of the annular sealrings 3, 4 may be the same or different. The continuity of the annulargroove 39 allows for uninterrupted communication of the gas into thediagonal grooves 19. The gas traverses the respective diagonal grooves19 and is redirected outward from the rotatable runner 15 at the outletend 46 of each diagonal groove 19. The gas exits the left-side diagonalgroove 19 and impinges the first annular seal ring 3 forming a thin-filmlayer 20 between the first annular seal ring 3 and rotatable runner 15,thereby separating the first annular seal ring 3 from the rotatablerunner 15. The gas exits the right-side diagonal groove 19 and impingesthe second annular seal ring 4 forming a thin-film layer 20 between thesecond annular seal ring 4 and rotatable runner 15, thereby separatingthe second annular seal ring 4 from the rotatable runner 15.

Referring now to FIG. 4, a seal assembly 21 is shown with an annularseal housing 22, a first annular seal ring 23, a second annular sealring 24, and a center ring 25, each disposed so as to becircumferentially arranged about a rotatable runner 35 (see FIG. 5).Components are composed of materials understood in the art. Therotatable runner 35 is an element known within the art attached to arotatable shaft (not shown). The rotatable runner 35 is rotatable withinthe turbine engine via the shaft. A seal is formed along the rotatablerunner 35 by each annular seal ring 23, 24. The annular seal housing 22,annular seal rings 23, 24, center ring 25, and rotatable runner 35 arealigned along and disposed about a centerline 34, often coinciding witha rotational axis along a turbine engine. The annular seal housing 22 isattached to components comprising the housing structure 51 (generallyshown) of a turbine engine fixing the annular seal housing 22 thereto.The housing structure 51 is stationary and therefore non-rotating. Thehousing structure 51, seal assembly 21, and the rotatable runner 35generally define at least a first compartment 5 and a second compartment6. The configuration of the housing structure 51 is design dependent;however, it is understood for purposes of the present invention that thehousing structure 51 cooperates with the seal assembly 1 and rotatablerunner 35 to define two separate compartments whereby a gas resides at alow pressure within one such compartment 5 and a lubricant resides atlow pressure within another compartment 6.

The annular seal housing 22 generally defines a pocket within which theannular seal rings 23, 24 and center ring 25 reside. The annular sealhousing 22 could have a U-shaped cross-section opening inward toward thecenterline 34. One end of the annular seal housing 22 could include aninsert 27 and a retaining ring 28 which allow for assembly/disassemblyof the annular seal rings 23, 24 and center ring 25 onto the annularseal housing 22. The annular seal rings 23, 24 could be fixed to theannular seal housing 22 via means known within the art to limit or toprevent relative rotational motion between the annular seal rings 23, 24and the annular seal housing 22. In one non-limiting example, a pair ofanti-rotation pins 52 is secured to the annular seal housing 22 toseparately engage a pocket 53 along each of the first and second annularseal rings 23, 24. Interaction between anti-rotation pin 52 and pocket53 functions as a positive stop to restrict rotation of each of thefirst and second annular seal rings 23, 24 with respect to the annularseal housing 22.

The first and second annular seal rings 23, 24 are ring-shaped elements.Each annular seal ring 23, 24 could comprise at least two arcuatesegments which form a generally circular-shaped ring when assembledabout a rotatable runner 35. The segmented construction of the first andsecond annular seal rings 3, 4 allows for radial expansion andcontraction by the respective annular seal rings 23, 24 about arotatable runner 35. Each annular seal ring 23, 24, is generally biasedtoward a rotatable runner 35 via a compressive force applied by a garterspring 29, 30. The garter spring 29, 30 could contact the outercircumference of the respective annular seal ring 23, 24 and apply thecompressive force inward toward the rotatable runner 35.

The center ring 25 is interposed between the first and second annularseal rings 23, 24 within the annular seal housing 22. A plurality offirst springs 32 are interposed between the first annular seal ring 23and the center ring 25. A plurality of second springs 33 are interposedbetween the second annular seal ring 24 and the center ring 25. Thefirst and second springs 32, 33 could be evenly spaced about thecircumference of the respective annular seal rings 23, 24 so as to exerta generally uniform separation force onto each annular seal ring 23, 24with respect to the center ring 25. The first and second springs 32, 33could be a coil-type device which generally resists compression. Eachspring 32, 33 could be attached or fixed to the respective annular sealring 23, 24. For example, one end of each first and second spring 32, 33could be partially recessed within a pocket 54 along the respectiveannular seal ring 23, 24. First and second springs 32, 33 should besufficiently long so as to at least partially compress when assembledbetween the respective annular seal rings 23, 24 and center ring 25.First and second springs 32, 33 should exert a force onto the annularseal rings 23, 24 causing the annular seal rings 23, 24 to separate fromthe center ring 25, thereby pressing the annular seal rings 23, 24 ontoopposite sides of the annular seal housing 22 with the center ring 25substantially centered between the annular seal rings 23, 24. Theseparation force exerted by the compression springs 32, 33 could form anoptional gap (not shown) between the center ring 25 and each annularseal ring 23, 24.

At least one inlet 26 is disposed along an outer wall of the annularseal housing 22. The inlet(s) 26 is/are positioned so as to at leastpartially overlay the center ring 25 between the annular seal rings 23,24. Two or more inlets 26 could be uniformly positioned about thecircumference of the annular seal housing 22. Each inlet 26 is a pathwaythrough which a gas is communicated between the annular seal rings 23,24.

In some embodiments, the center ring 25 could include a plurality ofholes 31 traversing the radial dimension of the center ring 25. Theholes 31 could be evenly spaced about the circumference of the centerring 25 and positioned so as to at least partially overlay the inlet(s)26.

Although various embodiments are described including a center ring 25,it is understood that the center ring 25 is an optional feature and thatsuch embodiments could include the gap 13 arrangement shown in FIG. 1.

Referring now to FIG. 5, a seal assembly 21 is shown in cross-sectionalform disposed about a rotatable runner 35, the latter illustrated inside-view form, between a pair of compartments 5, 6. The rotatablerunner 35 includes a plurality of groove structures 37. The groovestructures 37 are arranged circumferentially along the outer annularsurface 36 of the rotatable runner 35 immediately adjacent to the sealassembly 21. The groove structures 37 are positioned so as tocommunicate a gas onto the annular seal rings 23, 24 as the rotatablerunner 35 rotates with respect to the seal assembly 21. In someembodiments, it might be advantageous for adjacent grooves structures 37to partially overlap as represented in FIG. 5. In other embodiments,adjacent groove structures 37 could be arranged in an end-to-endconfiguration or with a separation between the end of one groovestructure 37 and the start of the next groove structure 37.

Each groove structure 37 further includes a pair of diagonal grooves 38disposed about a central axis 44 circumferentially along an outerannular surface 36 of the rotatable runner 35. The diagonal grooves 38could be aligned symmetrically or non-symmetrically about the centralaxis 44. Each diagonal groove 38 is a channel, depression, flute, or thelike disposed along the outer annular surface 36. Although the diagonalgrooves 38 are represented as linear elements, it is understood thatother designs are possible including multi-linear and non-linearconfigurations. The central axis 44 could align with the center ring 25between first and second annular seal rings 23, 24 or reside adjacent tothe first and second annular seal rings 23, 24 to allow communication ofa gas onto the groove structures 37 over the translational range of therotatable runner 35. The diagonal grooves 38 are oriented so that thetop of the left-side diagonal groove 38 extends toward the right and thetop of the right-side diagonal groove 38 extends toward the left. Theinward oriented ends of the diagonal grooves 38 intersect along or nearthe central axis 44 to form an apex 40. The apex 40 is further orientedtoward the rotational direction of the rotatable runner 35 so that thediagonal grooves 38 expand outward opposite of the rotational direction.The dimensions and angular orientation of the diagonal grooves 38 andthe apex 40 are design dependent and based in part on the translationalrange of the rotatable runner 35, the widths of the annular seal rings23, 24, center ring 25 and optional hole 31, the extent of overlap ornon-overlap between adjacent groove structures 37, the pressure requiredto adequately seal the interface between the rotatable runner 35 andannular seal rings 23, 24, and/or other design factors.

Each diagonal groove 38 further includes at least two optional steps 62a-62 d. Although four steps 62 a-62 d are illustrated along eachdiagonal groove 38 in FIG. 5, it is understood that two or more suchsteps 62 a-62 d may reside along each diagonal groove 38. Each step 62a-62 d corresponds to a change in the local depth of the diagonal groove38 relative to the outer annular surface 36. For example, if a diagonalgroove 38 includes two steps 62 a, 62 b, then one step 62 a would have afirst depth and another step 62 b would have a second depth. The depthsdiffer so that one depth is deeper and another depth is shallower. Inpreferred arrangements, the steps 62 a-62 d are arranged so that thechange in local depth from one step to another step results in astepwise variation along the length of each diagonal groove 38.

When the diagonal grooves 38 intersect at an apex 40 or the like, thefirst step 62 a may be located at the apex 40 and immediately adjacentto and communicable with the next step 62 b along each diagonal groove38 extending from the apex 40, as illustrated in FIG. 5. In otherembodiments, two or more steps may reside within the apex 40 and atleast one step along each diagonal groove 38. In yet other embodiments,one step 62 a may reside along the apex 40 and a portion of one or morediagonal grooves 38 and the remaining step(s) 62 b reside(s) exclusivelyalong each diagonal groove 38. Regardless of the exact arrangement, thesteps 62 a-62 d are arranged consecutively to effect a stepwisevariation of the depth along the length of each groove structure 37.

Referring again to FIG. 5, a gas enters the inlet(s) 26 and is directedinward onto the center ring 25. The gas flows around the center ring 25traversing the gaps between the center ring 25 and the first and secondannular seal rings 23, 24 when the center ring 25 does not include theoptional holes 31. The gas traverses the holes 31 when the center ring25 includes the optional holes 31. Next, the gas impinges the outerannular surface 36 of the rotatable runner 35, preferably at or near theapex 40 or inlet end 45. The gas enters the apex 40 or inlet end 45 andis bifurcated by the groove structure 37 so that a first portion isdirected into the left-side diagonal groove 38 and a second portion isdirected into the right-side diagonal groove 38. The quantity and/orrate of gas communicated onto each of the annular seal rings 23, 24 maybe the same or different. The gas traverses the respective diagonalgrooves 38 and is redirected outward from the rotatable runner 35 at theoutlet end 46 of each diagonal groove 38. The gas exits the left-sidediagonal groove 38 and impinges the first annular seal ring 23 forming athin-film layer 20 between the first annular seal ring 23 and rotatablerunner 35, thereby separating the first annular seal ring 23 from therotatable runner 35. The gas exits the right-side diagonal groove 38 andimpinges the second annular seal ring 24 forming a thin-film layer 20between the second annular seal ring 24 and rotatable runner 35, therebyseparating the second annular seal ring 24 from the rotatable runner 35.

Referring now to FIG. 6, a seal assembly 21 is shown in cross-sectionalform disposed about a rotatable runner 35, the latter illustrated inside-view form, between a pair of compartments 5, 6. The rotatablerunner 35 includes a plurality of groove structures 37. The groovestructures 37 are arranged circumferentially along the outer annularsurface 36 of the rotatable runner 35 immediately adjacent to the sealassembly 21. The groove structures 37 are positioned so as tocommunicate a gas onto the annular seal rings 23, 24 as the rotatablerunner 35 rotates with respect to the seal assembly 21. In someembodiments, it might be advantageous for adjacent grooves structures 37to partially overlap as represented in FIG. 6. In other embodiments,adjacent groove structures 37 could be arranged in an end-to-endconfiguration or with a separation between the end of one groovestructure 37 and the start of the next groove structure 37.

Each groove structure 37 further includes a pair of diagonal grooves 38disposed about a central axis 44 circumferentially along an outerannular surface 36 of the rotatable runner 35. The diagonal grooves 38could be aligned symmetrically or non-symmetrically about the centralaxis 44. Each diagonal groove 38 is a channel, depression, flute, or thelike disposed along the outer annular surface 36. Although the diagonalgrooves 38 are represented as linear elements, it is understood thatother designs are possible including multi-linear and non-linearconfigurations. The central axis 44 could align with the center ring 25between first and second annular seal rings 23, 24 or reside adjacent tothe first and second annular seal rings 23, 24 to allow communication ofa gas onto the groove structures 37 over the translational range of therotatable runner 35. The diagonal grooves 38 are oriented so that thetop of the left-side diagonal groove 38 extends toward the right and thetop of the right-side diagonal groove 38 extends toward the left. Theinward oriented ends of the diagonal grooves 38 are separately disposedabout the central axis 44 so that the diagonal grooves 38 expand outwardopposite of the rotational direction. The dimensions and angularorientation of the diagonal grooves 38 are design dependent and based inpart on the translational range of the rotatable runner 35, the widthsof the annular seal rings 23, 24, center ring 25 and optional hole 31,the extent of overlap or non-overlap between adjacent groove structures37, the pressure required to adequately seal the interface between therotatable runner 35 and annular seal rings 23, 24, and/or other designfactors.

Each diagonal groove 38 further includes at least two optional steps 62a-62 d. Although four steps 62 a-62 d are illustrated along eachdiagonal groove 38 in FIG. 6, it is understood that two or more suchsteps 62 a-62 d may reside along each diagonal groove 38. Each step 62a-62 d corresponds to a change in the local depth of the diagonal groove38 relative to the outer annular surface 36. For example, if a diagonalgroove 38 includes two steps 62 a, 62 b, then one step 62 a would have afirst depth and another step 62 b would have a second depth. The depthsdiffer so that one depth is deeper and another depth is shallower. Inpreferred arrangements, the steps 62 a-62 d are arranged so that thechange in local depth from one step to another step results in astepwise variation along the length of each diagonal groove 38.Regardless of the exact arrangement, the steps 62 a-62 d are arrangedconsecutively to effect a stepwise variation of the depth along thelength of each groove structure 37.

Referring again to FIG. 6, a gas enters the inlet(s) 26 and is directedinward onto the center ring 25. The gas flows around the center ring 25traversing the gaps between the center ring 25 and the first and secondannular seal rings 23, 24 when the center ring 25 does not include theoptional holes 31. The gas traverses the holes 31 when the center ring25 includes the optional holes 31. Next, the gas impinges the outerannular surface 36 of the rotatable runner 35, preferably at or nearinlet ends 45. The gas is bifurcated by the groove structure 37 at theinlet ends 45 so that a first portion is directed into the left-sidediagonal groove 38 and a second portion is directed into the right-sidediagonal groove 38. The quantity and/or rate of gas communicated ontoeach of the annular seal rings 23, 24 may be the same or different. Thegas traverses the respective diagonal grooves 38 and is redirectedoutward from the rotatable runner 35 at the outlet end 46 of eachdiagonal groove 38. The gas exits the left-side diagonal groove 38 andimpinges the first annular seal ring 23 forming a thin-film layer 20between the first annular seal ring 23 and rotatable runner 35, therebyseparating the first annular seal ring 23 from the rotatable runner 35.The gas exits the right-side diagonal groove 38 and impinges the secondannular seal ring 24 forming a thin-film layer 20 between the secondannular seal ring 24 and rotatable runner 35, thereby separating thesecond annular seal ring 24 from the rotatable runner 35.

Referring now to FIG. 7, a seal assembly 21 is shown in cross-sectionalform disposed about a rotatable runner 35, the latter illustrated inside-view form, between a pair of compartments 5, 6. The rotatablerunner 35 includes a plurality of groove structures 41. The groovestructures 41 are arranged circumferentially along the outer annularsurface 36 of the rotatable runner 35 immediately adjacent to the sealassembly 21. The groove structures 41 are positioned so as tocommunicate a gas onto the annular seal rings 23, 24 as the rotatablerunner 35 rotates with respect to the seal assembly 21. In someembodiments, it might be advantageous for adjacent grooves structures 41to partially overlap. In other embodiments, adjacent groove structures41 could be arranged in an end-to-end configuration or with a separationbetween the end of one groove structure 41 and the start of the nextgroove structure 41, the latter represented in FIG. 7.

Each groove structure 41 further includes a plurality of diagonalgrooves 43 disposed about a central axis 44 circumferentially along anouter annular surface 36 of the rotatable runner 35. The diagonalgrooves 43 could be aligned symmetrically or non-symmetrically about thecentral axis 44. Each diagonal groove 43 is a channel, depression,flute, or the like disposed along the outer annular surface 36. Althoughthe diagonal grooves 43 are represented as linear elements, it isunderstood that other designs are possible including multi-linear andnon-linear configurations. The central axis 44 could align with thecenter ring 25 between first and second annular seal rings 23, 24 orreside adjacent to the first and second annular seal rings 23, 24 toallow communication of a gas onto the groove structures 41 over thetranslational range of the rotatable runner 35. The diagonal grooves 43are oriented so that the top of each left-side diagonal groove 43extends toward the right and the top of each right-side diagonal groove43 extends toward the left. The inward oriented ends of the diagonalgrooves 43 are separately disposed about the central axis 44 so that thediagonal grooves 43 expand outward opposite of the rotational direction.

At least two diagonal grooves 43 are disposed along each side of thecentral axis 44. In some embodiments, the diagonal grooves 43 could besubstantially parallel to other diagonal grooves 43 along the same sideof the central axis 44 as represented by the set of three diagonalgrooves 43 along each side of the central axis 44 in FIG. 7. In otherembodiments, the diagonal grooves 43 could be oriented at two or moreangles with respect to the rotational direction and/or central axis 44whereby the diagonal grooves 43 along the same side of the central axis44 are non-parallel. It is also possible in some embodiments for theinlet ends 45 and the outlet ends 46 to be aligned circumferentially asrepresented in FIG. 7. In yet other embodiments, the inlet ends 45 andthe outlet ends 46 could be skewed or staggered and/or the diagonalgrooves 43 have the same or different lengths.

The dimensions, angular orientation and number of the diagonal grooves43 are design dependent and based in part on the translational range ofthe rotatable runner 35, the widths of the annular seal rings 23, 24,center ring 25 and optional hole 31, the extent of overlap ornon-overlap between adjacent groove structures 41, the number of flowsfrom a groove structure 41 required to impinge each annular seal ring23, 24, the pressure required to adequately seal the interface betweenthe rotatable runner 35 and annular seal rings 23, 24, and/or otherdesign factors.

Each diagonal groove 43 further includes at least two optional steps 62a-62 d. Although four steps 62 a-62 d are illustrated along eachdiagonal groove 43 in FIG. 7, it is understood that two or more suchsteps 62 a-62 d may reside along each diagonal groove 43. Each step 62a-62 d corresponds to a change in the local depth of the diagonal groove43 relative to the outer annular surface 36. For example, if a diagonalgroove 43 includes two steps 62 a, 62 b, then one step 62 a would have afirst depth and another step 62 b would have a second depth. The depthsdiffer so that one depth is deeper and another depth is shallower. Inpreferred arrangements, the steps 62 a-62 d are arranged so that thechange in local depth from one step to another step results in astepwise variation along the length of each diagonal groove 43.Regardless of the exact arrangement, the steps 62 a-62 d are arrangedconsecutively to effect a stepwise variation of the depth along thelength of each groove structure 41.

Referring again to FIG. 7, a gas enters the inlet(s) 26 and is directedinward onto the center ring 25. The gas flows around the center ring 25traversing the gaps between the center ring 25 and the first and secondannular seal rings 23, 24 when the center ring 25 does not include theoptional holes 31. The gas traverses the holes 31 when the center ring25 includes the optional holes 31. Next, the gas impinges the outerannular surface 36 of the rotatable runner 35, preferably at or nearinlet ends 45. The gas is bifurcated by the groove structure 41 at theinlet ends 45 so that a first portion is directed into the left-sidediagonal grooves 43 and a second portion is directed into the right-sidediagonal grooves 43. The quantity and/or rate of gas communicated ontoeach of the annular seal rings 23, 24 may be the same or different. Thegas traverses the respective diagonal grooves 43 and is redirectedoutward from the rotatable runner 35 at the outlet end 46 of eachdiagonal groove 43. The gas exits at least one left-side diagonal groove43 within a groove structure 41 and impinges the first annular seal ring23 forming a thin-film layer 20 between the first annular seal ring 23and rotatable runner 35, thereby separating the first annular seal ring23 from the rotatable runner 35. The gas exits at least one right-sidediagonal groove 43 within a groove structure 41 and impinges the secondannular seal ring 24 forming a thin-film layer 20 between the secondannular seal ring 24 and rotatable runner 35, thereby separating thesecond annular seal ring 24 from the rotatable runner 35.

Referring now to FIG. 8, a seal assembly 21 is shown in cross-sectionalform disposed about a rotatable runner 35, the latter illustrated inside-view form, between a pair of compartments 5, 6. The rotatablerunner 35 includes a plurality of groove structures 41. The groovestructures 41 are arranged circumferentially along the outer annularsurface 36 of the rotatable runner 35 immediately adjacent to the sealassembly 21. The groove structures 41 are positioned so as tocommunicate a gas onto the annular seal rings 23, 24 as the rotatablerunner 35 rotates with respect to the seal assembly 21. In someembodiments, it might be advantageous for adjacent grooves structures 41to partially overlap. In other embodiments, adjacent groove structures41 could be arranged in an end-to-end configuration or with a separationbetween the end of one groove structure 41 and the start of the nextgroove structure 41, the latter represented in FIG. 8.

Each groove structure 41 further includes at least two of diagonalgrooves 43 disposed about a central axis 44 circumferentially along anouter annular surface 36 of the rotatable runner 35. The diagonalgrooves 43 could be aligned symmetrically or non-symmetrically about thecentral axis 44. Each diagonal groove 43 is a channel, depression,flute, or the like disposed along the outer annular surface 36. Althoughthe diagonal grooves 43 are represented as linear elements, it isunderstood that other designs are possible including multi-linear andnon-linear configurations. The central axis 44 could align with thecenter ring 25 between first and second annular seal rings 23, 24 orreside adjacent to the first and second annular seal rings 23, 24 toallow communication of a gas onto the groove structures 41 over thetranslational range of the rotatable runner 35. The diagonal grooves 43are oriented so that the top of each left-side diagonal groove 43extends toward the right and the top of each right-side diagonal groove43 extends toward the left. The inward oriented ends of the diagonalgrooves 43 are separately disposed about the central axis 44 so that thediagonal grooves 43 expand outward opposite of the rotational direction.

At least one diagonal groove 43 is disposed along each side of thecentral axis 44. When two or more diagonal grooves 43 are disposed alongeach side of the central axis 44, the diagonal grooves 43 could besubstantially parallel to other diagonal grooves 43 along the same sideof the central axis 44 as represented by the set of three diagonalgrooves 43 along each side of the central axis 44 in FIG. 8. In otherembodiments, the diagonal grooves 43 could be oriented at two or moreangles with respect to the rotational direction and/or central axis 44whereby the diagonal grooves 43 along the same side of the central axis44 are non-parallel. Two or more of the inlet ends 45 and the outletends 46 could be aligned circumferentially as represented in FIG. 8. Twoor more of other inlet ends 45 and outlet ends 46 could be skewed orstaggered as also represented in FIG. 8. Two or more diagonal grooves 43could have the same or different lengths as further represented in FIG.8.

Two or more diagonal grooves 43 could communicate with a feed groove 42at the inlet ends 45 of the diagonal grooves 43. The feed groove 42 is achannel, depression, flute, or the like disposed along the outer annularsurface 36. Although the feed groove 42 is represented as a linearelement, it is understood that other designs are possible includingmulti-linear and non-linear configurations. The feed groove 42 isgenerally oriented to traverse the central axis 44 so as tocommunication with diagonal grooves 43 along both sides of the groovestructure 41. The feed groove 42 could be substantially perpendicular tothe rotational direction of the rotatable runner 35 and/or the centralaxis 44 as represented in FIG. 8. In other embodiments the feed groove42 could be obliquely oriented with respect to the rotational directionand/or central axis 44. When less than all diagonal grooves 43communicate with a feed groove 42 it is possible for the diagonalgrooves 43 to intersect as described in FIGS. 2 and 5 to form asecondary groove structure 55 within the larger primary groove structure41, as represented in FIG. 8.

The dimensions, angular orientation and number of the diagonal grooves43 and feed groove 42 are design dependent and based in part on thetranslational range of the rotatable runner 35, the widths of theannular seal rings 23, 24, center ring 25 and optional hole 31, theextent of overlap or non-overlap between adjacent groove structures 41with or without secondary groove structures 55, the number of flows froma groove structure 41 required to impinge each annular seal ring 23, 24,the pressure required to adequately seal the interface between therotatable runner 35 and annular seal rings 23, 24, and/or other designfactors.

Each diagonal groove 43 further includes at least two optional steps 62a-62 d. Although three or four steps 62 a-62 d are illustrated along thediagonal grooves 43 in FIG. 8, it is understood that two or more suchsteps 62 a-62 d may reside along each diagonal groove 43. Each step 62a-62 d corresponds to a change in the local depth of the diagonal groove43 relative to the outer annular surface 36. For example, if a diagonalgroove 43 includes two steps 62 a, 62 b, then one step 62 a would have afirst depth and another step 62 b would have a second depth. The depthsdiffer so that one depth is deeper and another depth is shallower. Inpreferred arrangements, the steps 62 a-62 d are arranged so that thechange in local depth from one step to another step results in astepwise variation along the length of each diagonal groove 43.

When the diagonal grooves 43 intersect at an apex as otherwise describedherein or a feed groove 40, the first step 62 a may be located at theapex or the feed groove 40 and immediately adjacent to and communicablewith the next step 62 b along each diagonal groove 43, as illustrated inFIG. 8. In other embodiments, two or more steps may reside within theapex or the feed groove 40 and at least one step along each diagonalgroove 43. In yet other embodiments, one step 62 a may reside along theapex or the feed groove 40 and a portion of one or more diagonal grooves43 and the remaining step(s) 62 b reside(s) exclusively along eachdiagonal groove 43, as also illustrated in FIG. 8. Regardless of theexact arrangement, the steps 62 a-62 d are arranged consecutively toeffect a stepwise variation of the depth along the length of each groovestructure 41 and each secondary groove structure 55.

Referring again to FIG. 8, a gas enters the inlet(s) 26 and is directedinward onto the center ring 25. The gas flows around the center ring 25traversing the gaps between the center ring 25 and the first and secondannular seal rings 23, 24 when the center ring 25 does not include theoptional holes 31. The gas traverses the holes 31 when the center ring25 includes the optional holes 31. Next, the gas impinges the feedgroove 42 along the outer annular surface 36 of the rotatable runner 35.The gas is bifurcated along the feed groove 42 allowing the gas to enterthe inlet ends 45 so that a first portion is directed into the left-sidediagonal grooves 43 and a second portion is directed into the right-sidediagonal grooves 43. The quantity and/or rate of gas communicated ontoeach of the annular seal rings 23, 24 may be the same or different. Thegas traverses the respective diagonal grooves 43 and is redirectedoutward from the rotatable runner 35 at the outlet end 46 of eachdiagonal groove 43. The gas exits at least one left-side diagonal groove43 within a groove structure 41 and impinges the first annular seal ring23 forming a thin-film layer 20 between the first annular seal ring 23and rotatable runner 35, thereby separating the first annular seal ring23 from the rotatable runner 35. The gas exits at least one right-sidediagonal groove 43 within a groove structure 41 and impinges the secondannular seal ring 24 forming a thin-film layer 20 between the secondannular seal ring 24 and rotatable runner 35, thereby separating thesecond annular seal ring 24 from the rotatable runner 35. The flowcharacteristics of the secondary groove structure 55 are as describedfor FIGS. 2 and 5.

Referring now to FIG. 9, a seal assembly 21 is shown in cross-sectionalform disposed about a rotatable runner 35, the latter illustrated inside-view form, between a pair of compartments 5, 6. The rotatablerunner 35 includes a plurality of groove structures 41. The groovestructures 41 are arranged circumferentially along the outer annularsurface 36 of the rotatable runner 35 immediately adjacent to the sealassembly 21. The groove structures 41 are positioned so as tocommunicate a gas onto the annular seal rings 23, 24 as the rotatablerunner 35 rotates with respect to the seal assembly 21. In someembodiments, it might be advantageous for adjacent grooves structures 41to partially overlap. In other embodiments, adjacent groove structures41 could be arranged in an end-to-end configuration or with a separationbetween the end of one groove structure 41 and the start of the nextgroove structure 41, the latter represented in FIG. 9.

Each groove structure 41 further includes at least two diagonal grooves43 disposed about a central axis 44 circumferentially along an outerannular surface 36 of the rotatable runner 35. The diagonal grooves 43could be aligned symmetrically or non-symmetrically about the centralaxis 44. Each diagonal groove 43 is a channel, depression, flute, or thelike disposed along the outer annular surface 36. Although the diagonalgrooves 43 are represented as linear elements, it is understood thatother designs are possible including multi-linear and non-linearconfigurations. The central axis 44 could align with the center ring 25between first and second annular seal rings 23, 24 or reside adjacent tothe first and second annular seal rings 23, 24 to allow communication ofa gas onto the groove structures 41 over the translational range of therotatable runner 35. The diagonal grooves 43 are oriented so that thetop of each left-side diagonal groove 43 extends toward the right andthe top of each right-side diagonal groove 43 extends toward the left.The inward oriented ends of the diagonal grooves 43 are separatelydisposed about the central axis 44 so that the diagonal grooves 43expand outward opposite of the rotational direction.

At least two diagonal grooves 43 are disposed along each side of thecentral axis 44. The diagonal grooves 43 could be substantially parallelto other diagonal grooves 43 along the same side of the central axis 44as represented by the set of three diagonal grooves 43 along each sideof the central axis 44 in FIG. 9. In other embodiments, the diagonalgrooves 43 could be oriented at two or more angles with respect to therotational direction and/or central axis 44 whereby the diagonal grooves43 along the same side of the central axis 44 are non-parallel. Two ormore of the inlet ends 45 and the outlet ends 46 could be alignedcircumferentially as represented in FIG. 9. Two or more inlet ends 45and outlet ends 46 could be skewed or staggered. Two or more diagonalgroove 43 could have the same or different lengths.

Two or more diagonal grooves 43 could communicate with a first feedgroove 56 at the inlet ends 45 of the left-side diagonal grooves 43. Twoor more other diagonal grooves 43 could communicate with a second feedgroove 57 at the inlet ends 45 of the right-side diagonal grooves 43.Each first and second feed groove 56, 57 is a channel, depression,flute, or the like disposed along the outer annular surface 36. Althoughthe feed grooves 56, 57 are represented as linear elements, it isunderstood that other designs are possible including multi-linear andnon-linear configurations. The feed grooves 56, 57 are separatelyoriented to either side of the central axis 44. The feed grooves 56, 57could be substantially perpendicular or oblique to the rotationaldirection and/or central axis 44, the former represented in FIG. 9.

The dimensions, angular orientation and number of the diagonal grooves43 and feed grooves 56, 57 are design dependent and based in part on thetranslational range of the rotatable runner 35, the widths of theannular seal rings 23, 24, center ring 25 and optional hole 31, theextent of overlap or non-overlap between adjacent groove structures 41,the number of flows from a groove structure 41 required to impinge eachannular seal ring 23, 24, the pressure required to adequately seal theinterface between the rotatable runner 35 and annular seal rings 23, 24,and/or other design factors.

Each diagonal groove 43 further includes at least two optional steps 62a-62 d. Although four steps 62 a-62 d are illustrated along the diagonalgrooves 43 in FIG. 9, it is understood that two or more such steps 62a-62 d may reside along each diagonal groove 43. Each step 62 a-62 dcorresponds to a change in the local depth of the diagonal groove 43relative to the outer annular surface 36. For example, if a diagonalgroove 43 includes two steps 62 a, 62 b, then one step 62 a would have afirst depth and another step 62 b would have a second depth. The depthsdiffer so that one depth is deeper and another depth is shallower. Inpreferred arrangements, the steps 62 a-62 d are arranged so that thechange in local depth from one step to another step results in astepwise variation along the length of each diagonal groove 43.

When the diagonal grooves 43 intersect a first feed groove 56 or asecond feed groove 57, the first step 62 a may be located at the firstfeed groove 56 or the second feed groove 57 and immediately adjacent toand communicable with the next step 62 b along each diagonal groove 43.In other embodiments, two or more steps may reside within the first feedgroove 56 or the second feed groove 57 and at least one step along eachdiagonal groove 43. In yet other embodiments, one step 62 a may residealong the first feed groove 56 or the second feed groove 57 and aportion of one or more diagonal grooves 43 and the remaining step(s) 62b reside(s) exclusively along each diagonal groove 43, as illustrated inFIG. 9. Regardless of the exact arrangement, the steps 62 a-62 d arearranged consecutively to effect a stepwise variation of the depth alongthe length of each groove structure 41.

Referring again to FIG. 9, a gas enters the inlet(s) 26 and is directedinward onto the center ring 25. The gas flows around the center ring 25traversing the gaps between the center ring 25 and the first and secondannular seal rings 23, 24 when the center ring 25 does not include theoptional holes 31. The gas traverses the holes 31 when the center ring25 includes the optional holes 31. Next, the gas impinges along or nearthe feed grooves 56, 57 along outer annular surface 36 of the rotatablerunner 35. The gas is bifurcated by the groove structure 41 so as toseparately enter the first and second feed grooves 56, 57 so that afirst portion is directed into the inlet ends 45 of the left-sidediagonal grooves 43 and a second portion is directed into the inlet ends45 of the right-side diagonal grooves 43. The quantity and/or rate ofgas communicated onto each of the annular seal rings 23, 24 may be thesame or different. The gas traverses the respective diagonal grooves 43and is redirected outward from the rotatable runner 35 at the outlet end46 of each diagonal groove 43. The exits at least one left-side diagonalgroove 43 within a groove structure 41 and impinges the first annularseal ring 23 forming a thin-film layer 20 between the first annular sealring 23 and rotatable runner 35, thereby separating the first annularseal ring 23 from the rotatable runner 35. The gas exits at least oneright-side diagonal groove 43 within a groove structure 41 and impingesthe second annular seal ring 24 forming a thin-film layer 20 between thesecond annular seal ring 24 and rotatable runner 35, thereby separatingthe second annular seal ring 24 from the rotatable runner 35.

Referring now to FIGS. 10-13, several seal assemblies 1 are shown incross-sectional form disposed about a rotatable runner 15, the latterillustrated in side-view form, between a pair of compartments 5, 6. Therotatable runner 15 includes a plurality of groove structures 41. Thegroove structures 41 are arranged circumferentially along the outerannular surface 16 of the rotatable runner 15 immediately adjacent tothe seal assembly 1. The groove structures 41 are positioned so as tocommunicate a gas onto the annular seal rings 3, 4 as the rotatablerunner 15 rotates with respect to the seal assembly 1. In someembodiments, it might be advantageous for adjacent grooves structures 41to partially overlap. In other embodiments, adjacent groove structures41 could be arranged in an end-to-end configuration or with a separationbetween the end of one groove structure 41 and the start of the nextgroove structure 41, the latter represented in FIGS. 10-13.

Each groove structure 41 further includes at least two axial grooves 49disposed about a central axis 44 circumferentially along an outerannular surface 16 of the rotatable runner 15. The axial grooves 49could be aligned symmetrically or non-symmetrically about the centralaxis 44. Each axial groove 49 is a channel, depression, flute, or thelike disposed along the outer annular surface 16. Although the axialgrooves 49 are represented as linear elements, it is understood thatother designs are possible including multi-linear and non-linearconfigurations. The central axis 44 could align with the gap 13 betweenthe first and second annular seal rings 3, 4 or reside adjacent to thefirst and second annular seal rings 3, 4 to allow communication of a gasonto the groove structures 41 over the translational range of therotatable runner 15. The axial grooves 49 are oriented substantiallyparallel to the rotational direction of the rotatable runner 15 and/orthe central axis 44.

At least two axial grooves 49 are disposed along each side of thecentral axis 44. The axial grooves 49 could be substantially parallel toother axial grooves 49 along the same side of the central axis 44 asrepresented by the set of two or more axial grooves 49 along each sideof the central axis 44 in FIGS. 10-13. Two or more of the inlet ends 45and the outlet ends 46 could be aligned circumferentially as representedin FIGS. 10-13. It is also possible for the inlet ends 45 and the outletends 46 to be skewed or staggered and/or and the axial grooves 49 tohave the same or different lengths.

The axial grooves 49 communicate with a feed groove 42 at the inlet ends45 of the axial grooves 49. The feed groove 42 is a channel, depression,flute, or the like disposed along the outer annular surface 16. Althoughthe feed groove 42 is represented as a linear element, it is understoodthat other designs are possible including multi-linear and non-linearconfigurations. The feed groove 42 traverses the central axis 44. Thefeed groove 42 could be substantially perpendicular or oblique to therotational direction and/or central axis 44.

The dimensions, angular orientation and number of the axial grooves 49are design dependent and based in part on the translational range of therotatable runner 15, the widths of the annular seal rings 3, 4, theextent of overlap or non-overlap between adjacent groove structures 41,the number of flows from a groove structure 41 required to impinge eachannular seal ring 3, 4, the pressure required to adequately seal theinterface between the rotatable runner 15 and annular seal rings 3, 4,and/or other design factors.

An optional windback thread 47 could extend from the annular sealhousing 2 in the direction of the second compartment 6. The windbackthread 47 is an element known within the art that utilizes the shearforces produced by a rotating shaft to circumferentially wind a fluidalong one or more threads. The threads are disposed along the innerannular surface of the windback thread 47 and oriented so that a fluidenters the threads and is directed away from the annular seal rings 3, 4within a seal assembly 1. The windback thread 47 could be machined intothe annular seal housing 2 or mechanically attached or fastened theretoas a separate element via methods understood in the art. The windbackthread 47 is disposed about the runner 15 so as to overlay the runner 15without contact. A plurality of optional slots 48 are positioned alongone end of the rotatable runner 15 adjacent to the windback thread 47.The slots 48 could interact with the windback thread 47 to sling a fluidaway from the annular seal rings 3, 4 in the direction of the secondcompartment 6. Although shown with several embodiments, it is understoodthat an optional windback thread 47 is applicable to other embodimentsdescribed herein.

In some embodiments, it might be advantageous to taper the axial grooves49 as represent in FIG. 11. The axial groove 49 could include a width atthe inlet end 45 that is greater than the width at the outlet end 46 sothat the width decreases with distance along the axial groove 49. Thisarrangement progressively reduces the volume through which the gaspasses causing a gas to compress with distance along the axial groove49, thereby further increasing the pressure otherwise achieved along anaxial groove 49 with uniform width. This effect is also possible bytapering the axial groove 49 depthwise along the length of the axialgroove 49 so that the depth at the inlet end 45 is greater than thedepth at the outlet end 46.

In yet other embodiments, the groove structures 41 could vary widthwiseas represented in FIGS. 12 and 13. The width between adjacent groovestructures 41 could differ so that the axial width W1 of one groovestructure 41 is greater than the axial width W2 of the next groovestructure 41 resulting in an overhang 50. The overhang 50 facilitates astaggered arrangement of axial grooves 49 between adjacent groovestructures 41 when the total number of axial grooves 49 is the same ineach groove structure 41 as represented in FIG. 12 and when the totalnumbers of axial grooves 49 differ between groove structures 41 asrepresented in FIG. 13. Both embodiments increase sealing effects over agreater range of translations by a rotatable runner 15.

Each axial groove 49 further includes at least two optional steps 62a-62 d. Although four steps 62 a-62 d are illustrated along the axialgrooves 49 in FIGS. 10-13, it is understood that two or more such steps62 a-62 d may reside along each axial groove 49. Each step 62 a-62 dcorresponds to a change in the local depth of the axial groove 49relative to the outer annular surface 16. For example, if an axialgroove 49 includes two steps 62 a, 62 b, then one step 62 a would have afirst depth and another step 62 b would have a second depth. The depthsdiffer so that one depth is deeper and another depth is shallower. Inpreferred arrangements, the steps 62 a-62 d are arranged so that thechange in local depth from one step to another step results in astepwise variation along the length of each axial groove 49.

When the axial grooves 49 intersect a feed groove 42, the first step 62a may be located at the feed groove 42 and immediately adjacent to andcommunicable with the next step 62 b along each axial groove 49. Inother embodiments, two or more steps may reside within the feed groove42 and at least one step along each axial groove 49. In yet otherembodiments, one step 62 a may reside along the feed groove 42 and aportion of one or more axial grooves 49 and the remaining step(s) 62 breside(s) exclusively along each axial groove 49, as illustrated inFIGS. 10-13. Regardless of the exact arrangement, the steps 62 a-62 dare arranged consecutively to effect a stepwise variation of the depthalong the length of each groove structure 41.

Referring again to FIGS. 10-13, a gas enters the inlet(s) 9 and isdirected into the gap 13 between the annular seal rings 3, 4. The gastraverses the gap 13 thereafter impinging the feed groove 42 along outerannular surface 16 of the rotatable runner 15. The gas is bifurcatedalong the feed groove 42 allowing the gas to enter the inlet ends 45 sothat a first portion is directed into the left-side axial grooves 49 anda second portion is directed into the right-side axial grooves 49. Thequantity and/or rate of gas communicated onto each of the annular sealrings 3, 4 may be the same or different. The gas traverses therespective axial grooves 49 and is redirected outward from the rotatablerunner 15 at the outlet end 46 of each axial groove 49. The gas exits atleast one left-side axial groove 49 within a groove structure 41 andimpinges the first annular seal ring 3 forming a thin-film layer 20between the first annular seal ring 3 and rotatable runner 15, therebyseparating the first annular seal ring 3 from the rotatable runner 15.The gas exits at least one right-side axial groove 49 within a groovestructure 41 and impinges the second annular seal ring 4 forming athin-film layer 20 between the second annular seal ring 4 and rotatablerunner 15, thereby separating the second annular seal ring 4 from therotatable runner 15.

In some embodiments, it might be advantageous to direct a gas throughthe rotatable runner 15 or 35 rather than or in addition to between thefirst and second annular seal rings 3, 4 or 23, 24.

Referring now to FIGS. 14 and 15, a seal assembly 21 is shown incross-sectional form disposed about a rotatable runner 35, the latterillustrated in side-view form, between a first compartment 58 and asecond compartment 59. The first and second compartments 58, 59 couldinclude a low pressure gas. Gas within the second compartment 59 couldbe at a higher pressure than the first compartment 58. One or bothcompartments 58, 59 could further include a lubricant. The annular sealhousing 22 could include an optional windback thread 47 as illustratedin FIGS. 10-13.

The rotatable runner 35 includes a plurality of groove structures 41 andcould further include an optional flange 60. The groove structures 41are arranged circumferentially along the outer annular surface 36 of therotatable runner 35 immediately adjacent to the seal assembly 21. Thegroove structures 41 are positioned so as to communicate a gas onto theannular seal rings 23, 24 as the rotatable runner 35 rotates withrespect to the seal assembly 21. While FIG. 14 shows bifurcated groovestructures 41, it is understood that all groove structures 17, 37, 41,55 described herein are applicable to embodiments wherein a gas isdirected through a rotatable runner 15, 35. An optional center ring 25could be interposed between the first and second annular seal rings 23,24, as otherwise described herein. It is likewise possible for the sealassembly 21 to not include a center ring 25, as also described herein.

A plurality of through holes 61 are separately disposed about thecircumference of the rotatable runner 35, as represented in FIGS. 14 and15. Each through hole 61 could traverse the rotatable runner 35 so as toallow passage of a gas along one side of the rotatable runner 35 toanother side of the rotatable runner 35, preferably from a regionadjacent to the inner portion of the rotatable runner 35 and onto theouter annular surface 36 of the rotatable runner 35 adjacent to thegroove structures 41 and the first and second annular seal rings 23, 24.

The number, size, shape, location, and arrangement of the through holes61 should allow communication of a gas through the rotatable runner 35and onto the outer annular surface 36 so as to form a thin film 20between the first and second annular seal rings 23, 24 and the rotatablerunner 35. In some embodiments, it might be advantageous for eachthrough hole 61 to be elongated along the central axis 44 and alignedtherewith with one such through hole 61 interposed between each pairedarrangement of diagonal grooves 43, as represented in FIG. 14. Otherconfigurations are possible.

Each diagonal groove 43 further includes at least two optional steps 62a-62 d. Although four steps 62 a-62 d are illustrated along eachdiagonal groove 43 in FIG. 14, it is understood that two or more suchsteps 62 a-62 d may reside along each diagonal groove 43. Each step 62a-62 d corresponds to a change in the local depth of the diagonal groove43 relative to the outer annular surface 36. For example, if a diagonalgroove 43 includes two steps 62 a, 62 b, then one step 62 a would have afirst depth and another step 62 b would have a second depth. The depthsdiffer so that one depth is deeper and another depth is shallower. Inpreferred arrangements, the steps 62 a-62 d are arranged so that thechange in local depth from one step to another step results in astepwise variation along the length of each diagonal groove 43.Regardless of the exact arrangement, the steps 62 a-62 d are arrangedconsecutively to effect a stepwise variation of the depth along thelength of each groove structure 41.

Referring again to FIGS. 14 and 15, a gas enters the through holes 61along the rotatable runner 35 and is directed outward in the directionof the first and second annular seal rings 23, 24 with or without thecenter ring 25. The gas flows onto the rotatable runner 35 so as toimpinge the outer annular surface 36 of the rotatable runner 35,preferably at or near the inlet ends 45. The gas is bifurcated by thegroove structure 41 at the inlet ends 45 so that a first portion isdirected into the left-side diagonal grooves 43 and a second portion isdirected into the right-side diagonal grooves 43. The quantity and/orrate of gas communicated onto each of the annular seal rings 23, 24 maybe the same or different. The gas traverses the respective diagonalgrooves 43 and is redirected outward from the rotatable runner 35 at theoutlet end 46 of each diagonal groove 43. The gas exits at least oneleft-side diagonal groove 43 within a groove structure 41 and impingesthe first annular seal ring 23 forming a thin-film layer 20 between thefirst annular seal ring 23 and rotatable runner 35, thereby separatingthe first annular seal ring 23 from the rotatable runner 35. The gasexits at least one right-side diagonal groove 43 within a groovestructure 41 and impinges the second annular seal ring 24 forming athin-film layer 20 between the second annular seal ring 24 and rotatablerunner 35, thereby separating the second annular seal ring 24 from therotatable runner 35.

As described herein, a gas enters the diagonal or axial groove 19, 38,43 49 so that some or all of the gas entering the groove 19, 38, 43, 49either partially or completely traverses the length thereof. The inwardflow of the gas results in a pressure gradient. The result is a pressureprofile that steadily increases along the length of the groove 19, 38,43, 49 so that the pressure downstream is generally higher than thepressure upstream. The pressure profile may be linear, non-linear, or acombination thereof.

Referring now to FIGS. 16 and 17, exemplary radial and axial grooves 19,38, 43, 49 with four steps 62 a-62 d and five steps 62 a-62 e,respectively, are shown in an end-to-end configuration along the outerannular surface 16, 36 of a rotatable runner 15, 35. The steps 62 a-62d, 62 a-62 e form a single pocket-like structure that opens outward inthe direction of the outer annular surface 16, 36. FIG. 16 illustratesthe stepwise orientation of the steps 62 a-62 d whereby the first step62 a, second step 62 b, third step 62 c, and fourth step 62 d separatelyextend into the rotatable runner 15, 35 at four depths h_(a), h_(b),h_(c), h_(d), respectively. FIG. 17 illustrates the stepwise orientationof the steps 62 a-62 e whereby the first step 62 a, second step 62 b,third step 62 c, fourth step 62 d, and fifth step 62 e separately extendinto the rotatable runner 15, 35 at five depths h_(a), h_(b), h_(c),h_(d), h_(e) respectively. In preferred embodiments, the depths h_(a),h_(b), h_(c), h_(d) should decrease incrementally(h_(a)>h_(b)>h_(e)>h_(d)) in the direction opposite of the rotationaldirection of the rotatable runner 15, 35. However, it is only requiredthat at least one downstream step 62 b-62 d be at a depth less than oneupstream step 62 a-62 c. In other embodiments, it might be advantageousto include at least one downstream step 62 b-62 e at a depth h_(b),h_(c), h_(d), h_(e) greater than the depth h_(a), h_(b), h_(c), h_(d) ofat least one upstream steps 62 a-62 d. Referring again to FIGS. 16 and17, the depths h_(a), h_(b), h_(c), h_(d), h_(e) generally represent thedistance from the outer annular surface 16, 36 to the base 63 a-63 e ofeach respective step 62 a-62 e, although other methods of determiningthe depths h_(a), h_(b), h_(c), h_(d), h_(e) are possible. Each base 63a-63 e is defined by a surface of generally planar extent along therotatable runner 15, 35; however, other shapes are possible. The bases63 a-63 e may be oriented so that two or more such bases 63 a-63 e areparallel, as shown in FIGS. 16 and 17. Regardless of the shape andorientation of each base 63 a-63 e, the transition from one step 62 a-62d to another step 62 b-62 e defines a shoulder 64. The shoulder 64represents an abrupt change or discontinuity in the depth profilebetween the inlet and outlet end of the diagonal groove 19, 38, 43 andthe axial groove 49.

As the rotatable runner 15, 35 rotates, a gas adjacent to orcommunicated onto the rotatable runner 15, 35 flows into and along thesteps 62 a-62 e in the direction opposite to the rotational direction ofthe rotatable runner 15, 35. In addition to or in place of the flowpatterns implemented by the various groove structures 17, 37, 41, 55 asotherwise described herein, interaction between the gas and eachshoulder 64 redirects the circumferential flow along each step 62 a-62 eso that some or all of the gas is locally directed radially outwardtoward the first and second annular seal rings 3, 4 or 23, 24. Theresult is turbulent flow adjacent to each shoulder 64 causing localizedpressure discontinuities along the pressure profile described hereinthat enhance the thin-film layer 20 formed between the outer annularsurface 16, 36 and first and second annular seal rings 3, 4 or 23, 24.The enhanced stiffness of the resultant thin-film layer 20 allows forhigher operating differential pressures without the seal contacting therunner which extends seal life and lowers heat generation. The gas thatleaks thru the thin-film layer 20 prevents or minimizes a lubricant fromleaking into the sealing chamber and/or entering one or both lowerpressure compartments 5, 6.

Referring now to FIG. 18, a groove 19, 38, 43, 49 is shown along theouter annular surface 16, 36 of a rotatable runner 15, 35. The groove19, 38, 43, 49 is shown with steps 62 a-62 d arranged stepwise so thatthe deepest step 62 a is at the leftmost or upstream end and theshallowest step 62 d is at the rightmost or downstream end. The groove19, 38, 43, 49 is defined to include a length (L) centered with thecenterline 14, 34 so that one-half of the length (L) is to the left ofthe centerline 14, 34 and one-half of the length (L) is to the right ofthe centerline 14, 34. Each step 62 a-62 d has a unique depth (h)whereby the deepest groove defines the maximum depth (h_(max)) and theshallowest groove defines the minimum depth (h_(min)). The left end ofthe leftmost step 62 a and the right end of the rightmost step 62 dintersect the outer annular surface 16, 36 thereby defining a line 65.The line 65 intersects the radial distance (r), drawn from thecenterline 14, 34, at a right angle.

The location of each base 63 a-63 e may be defined as by distance ratio(R) representing the radial distance (r) adjusted by the depth (h) of astep 62 a-62 e over the runner radius r_(r). The distance ratio (R) iscalculated by the equation

$\begin{matrix}{R = \frac{r - h}{r_{r}}} & (1)\end{matrix}$where r is further calculated by the equation

$\begin{matrix}{r = \sqrt{r_{r}^{2} - \left( \frac{L}{2} \right)^{2}}} & (2)\end{matrix}$whereby the combination of equations (1) and (2) yields the equation

$\begin{matrix}{R = \frac{\sqrt{\left( {r_{r}^{2} - \left( \frac{L}{2} \right)^{2}} \right.} - h}{r_{r}}} & (3)\end{matrix}$

For purpose of Equation (3), the length (L) corresponds to the chord orcircumferential length as described in FIGS. 19a and 19b after allappropriate adjustments (if required) and the depth (h) of a groove 62a-62 e corresponds to the vertical distance between line 65 and the base63 a-63 e. If the base 63 a-63 e is non-planar or angled, then a maximumdepth or an average depth may be appropriate for calculational purposes.The lower and upper bounds for the distance ratio (R) for a groove 19,38, 43, 49 are calculable for a given length (L) and runner radius(r_(r)) where the lower distance ratio (R_(L)) corresponds to themaximum depth (h_(max)) and the upper distance ratio (R_(U)) correspondsto the minimum depth (h_(min)).

Referring now to FIG. 20, the lower distance ratio (R_(L)) and upperdistance ratio (R_(U)) are depicted for a variety of design variationsfor a runner radius (r_(r)) from 1-inches to 20-inches. The lowerdistance ratio (R_(L)) corresponds to a length (L) of 1.95-inches and amaximum step depth (h) of 0.1-inches. The upper distance ratio (R_(U))corresponds to a length (L) of 0.5-inches and a minimum step depth (h)of 0.00001-inches. The resultant lines define the design space forpotential distance ratios (R) when the runner radius (r_(r)) is from1-inch to 20-inches, the length (L) is from 0.5-inches to 1.95-inches,and the depth (h) is from 0.00001-inches to 0.1-inches.

The description above indicates that a great degree of flexibility isoffered in terms of the present invention. Although various embodimentshave been described in considerable detail with reference to certainpreferred versions thereof, other versions are possible. Therefore, thespirit and scope of the appended claims should not be limited to thedescription of the preferred versions contained herein.

What is claimed is:
 1. A circumferential back-to-back seal assembly withbifurcated flow comprising: (a) an annular seal housing disposed betweena pair of compartments; (b) a first annular seal ring; (c) a secondannular seal ring, said first annular seal ring and said second annularseal ring disposed within said annular seal housing; (d) a rotatablerunner, said first annular seal ring and said second annular seal ringdisposed around said rotatable runner; and (e) a plurality of groovestructures disposed along an outer annular surface of said rotatablerunner, a gas communicable onto said groove structures, each said groovestructure separates said gas so that a first portion of said gas isdirected onto said first annular seal ring to form a first thin-filmlayer between said rotatable runner and said first annular seal ring anda second portion of said gas is directed onto said second annular sealring to form a second thin-film layer between said rotatable runner andsaid second annular seal ring, each said groove structure having atleast two grooves, each said groove includes at least two adjoiningsteps wherein each said adjoining step has a base disposed at a depth,said depth decreases from at least one said adjoining step to anothersaid adjoining step in the direction opposite to rotation, a shoulderdisposed between two said adjoining steps, said shoulder locallyredirects said gas outward toward said first annular seal ring or saidsecond annular seal ring so that flow of said gas is turbulent, eachsaid groove tapered widthwise, said grooves separately disposed about acentral axis aligned adjacent to said first annular seal ring and saidsecond annular seal ring, said grooves disposed substantially parallelwith respect to rotational direction of said rotatable runner, saidgrooves communicable with a feed groove which directs said gas into saidgrooves.
 2. The circumferential back-to-back seal assembly of claim 1,wherein said depth increases from at least one said adjoining step toanother said adjoining step in the direction opposite to rotation. 3.The circumferential back-to-back seal assembly of claim 1, furthercomprising: (f) a plurality of springs disposed between and directlycontacts said first annular seal ring and said second annular seal ring,said springs separate said first annular seal ring and said secondannular seal ring.
 4. The circumferential back-to-back seal assembly ofclaim 1, further comprising: (f) a center ring disposed within saidannular seal housing between said first annular seal ring and saidsecond annular seal ring.
 5. The circumferential back-to-back sealassembly of claim 1, further comprising: (f) a center ring disposedwithin said annular seal housing between said first annular seal ringand said second annular seal ring; and (g) a plurality of springsdisposed between said center ring and each of said first annular sealring and said second annular seal ring, said springs separate said firstannular seal ring and said second annular seal ring away from saidcenter ring.
 6. The circumferential back-to-back seal assembly of claim1, wherein said grooves vary lengthwise.
 7. The circumferentialback-to-back seal assembly of claim 1, wherein adjacent said groovestructures vary widthwise.
 8. The circumferential back-to-back sealassembly of claim 1, wherein said grooves separately disposed about saidcentral axis aligned adjacent to said first annular seal ring and saidsecond annular seal ring, adjacent said groove structures vary in numberof said grooves.
 9. The circumferential back-to-back seal assembly ofclaim 1, wherein said annular seal housing includes a windback threadadjacent to said compartment including a lubricant, said windback threaddirects said lubricant away from said first annular seal ring and saidsecond annular seal ring.
 10. The circumferential back-to-back sealassembly of claim 9, wherein a plurality of slots positioned along saidrotatable runner cooperate with said windback thread to sling saidlubricant away from said first annular seal ring and said second annularseal ring.